Magnetic Reconnection in Plasmas; a Celestial Phenomenon in the Laboratory
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Magnetic Reconnection in Plasmas; a Celestial Phenomenon in the Laboratory
J Egedal, W Fox, N Katz,A Le, M Porkolab,
MIT, PSFC, Cambridge, MA
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• The problem of magnetic reconnection
• Reconnection in the Versatile Toroidal Facility– Experimental setup
– Experimental observation
– Electron kinetic effects
• Wind satellite data from the deep magnetotail– Kinetic effects
• The new closed configuration in VTF
• Conclusions
Outline
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The Versatile Toroidal Facility (VTF)
3.5 m
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The Versatile Toroidal Facility (VTF)
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The Versatile Toroidal Facility (VTF)
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A new closed cusp by internal coil. Passing electrons &
spontaneous reconnection events.
Two different magnetic configurations
A open cusp magnetic field. Fast reconnection by trapped
electrons. Wind observation
Both configurations have Bguide and toroidal symmetry 2d
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VTF open configuration plasmashave a trapping potential
Typical Parameters:ne ~ 2-3 1016 m-3
Te ~ 12 eV
Ti ~ 1 eV
Bt ~ 80 mT (800 G)
Bc ~ 0-10 mT
Open field lines intersect the vessel wall.
Electrons stream faster than ions, so plasma charges positive
Thermal electrons are electrostatically trapped
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Reconnection drive
– Electric field induced by a central solenoid
– The solenoid is driven by an LC circuit
– Vloop ~ 100 V
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Plasma response to driven reconnection
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The electrostatic potential
Experimentalpotential,
+70 V
-70 V
2BE B
-v gB
Electron flow:
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The electrostatic potential
Frozen in law isbroken where EB0
0 cusppolBE BE
Ideal Plasma:
BE
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J Egedal et al., PRL 90, (2003)
The electrostatic potential
Frozen in law isbroken where EB0
0 cusppolBE BE
Ideal Plasma:
c
BE
eoc l
The size of the electron diffusion region is
δ
δ (c
m)
ρcusp
cgo BBl /
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• Why is the experimental current density so small?
• Liouville/Vlasov’s equation: df/dt=0
• For a given (x0,v0), follow the orbit back in time to x1
• Particle orbits calculated using electrostatic
and magnetic fields consistent
with the experiment.
• Massively parallel code
evaluates f(x0,v0) = f(|v1|).
Kinetic modeling(1)
Computer Physics Communications , (2004)
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0 – 12 kA/m2
• The current is calculated as
• Theory consistent with measurements
(B-probe resolution: 1.5cm)
Kinetic modeling(2)
3
|||| vv dfj
Theory
Experiment
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• The problem of magnetic reconnection
• Reconnection in the Versatile Toroidal Facility– Experimental setup
– Experimental observation
– Kinetic effects
• Wind satellite data from the deep magnetotail– Kinetic effects
• The new closed configuration in VTF
• Conclusions
Outline
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M. Øieroset et al. Nature 412, (2001)
M. Øieroset et al. PRL 89, (2002)
Wind satellite observations in distant magnetotail, 60RE
• Measurements within the ion diffusion region reveal: Strong anisotropy in fe.
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M. Øieroset et al. Nature 412, (2001)
M. Øieroset et al. PRL 89, (2002)
Wind satellite observations in distant magnetotail, 60RE
• Measurements within the ion diffusion region reveal: Strong anisotropy in fe.
Log(f)
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A trapped electron in the magnetotail
The magnetic moment:B
m
2
v 2
B
m
2
)v-v( 2||
2
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• From Vlasov’s equation df/dt=0 f(x0,v0) = f(Eexit )
• Two types of orbits:
Drift kinetic modeling of Wind data
Passing: Trapped : =mv2/(2B)+… is constant
maxmin|| /1cos
v
vBBc
c
No cooling Cooling
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• Applying f(x0,v0) = f(|v1|) to an X-line geometry consistent with the Wind measurements
• A potential, needed for trapping at low energies
• Ion outflow: 400 km/s, consistent with acceleration in
Drift kinetic modeling of Wind data
~ -300V~ -800V~ -1150V
Theory Wind
Phys. Rev. Lett. 94, (2005) 025006
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• Applying f(x0,v0) = f(|v1|) to an X-line geometry consistent with the Wind measurements
• A potential, needed for trapping at low energies
• Ion outflow: 400 km/s, consistent with acceleration in
Drift kinetic modeling of Wind data
Theory Wind
Phys. Rev. Lett. 94, (2005) 025006
~ -1150V
f(x0,v0) = f(E0-q0), passing
= f(B), trapped
Cluster Obs.
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• The problem of magnetic reconnection
• Reconnection in the Versatile Toroidal Facility– Experimental setup
– Experimental observation
– Kinetic effects
• Wind satellite data from the deep magnetotail– Kinetic effects
• The new closed configuration in VTF
• Conclusions
Outline
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New closed magnetic configurations
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A new reconnection drive scenario
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Spontaneous reconnection
Phys. Rev. Lett. 98, (2007) 015003
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Sweet-Parker is out, E ≠ *j !
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Current channel expelled, J
Magnetic energy released
R
Bz
vA ~ 10 km/s
c/pi ~ 1m, s ~ 0.12m
4
-4
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t [µs]d
/dt [
V]
What Triggers Reconnection? R
[m
]
t [µs]Mode at f=50 kHz
d/dt [V]R
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Plasma outflows
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Rough energy balance
• Magnetic energy released ~ 0.5 × 6 10-6 H × (500A)2 ~ 0.8 J
• Electron energization ~ 500 A × 80V × 2 10-5s ~ 0.8 J
• Ion flows: ~ 24 eV × 21018m-3 ×0.06m3 ~ 0.48 J
Strong energizations of the ions
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Electrostatic (and magnetic) fluctuations observed during reconnection events
Loop voltage (V)
Fluctuation > 10 MHz (au)
Spectrogramf (MHz)
0 1t (ms)[Mar 22 shot 405,HPF 80kHz, scope B/W 150 MHz]
fLH ~ 10 MHz
fpi ~ 30 MHz
(off scale)
fpe ~ 10 GHz
fce ~ 1 GHz
800
0Plasma Current (A)
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Conclusions– Fast, collisionless driven reconnection observed in the
open cusp configuration– Classical Coulomb collisions are not important– The width of the diffusion region scales with cusp
– Solving Vlasov’s equation (using the measured profiles of E and B) provides current profiles consistent with the VTF measurements; the current is limited by electron trapping.
– Wind observations consistent with fast reconnection mediated by trapped electrons
– New closed configuration in VTF provides exciting
new parameter regimes and boundaries for future study of collisionless magnetic reconnection & the trigger problem.
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Thank you for your attention
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Future studies with the new configuration• Fast, bursty reconnection with closed boundaries and in the
presence of guide magnetic field can be studied (for the first time)
• What controls the rate of reconnection?
• How is reconnection “triggered”
• Huge parameter regime available: Scans possible in Bcusp, Bguide, Te, Ne, Erec.
• Spans collisional to collisionless regimes: e = 0.1 – 103 m
• High plasma pressure (compared to magnetic field): ~ 1
• Warm and magnetized ions.
• 3D magnetic geometries are easily implemented
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Upgrade of open Cusp
Existing configuration Fields of new in-vessel coils
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Upgrade of open Cusp
New total field
Ionization region
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Reconnection Experiments with a Guide Magnetic Field
J Egedal, W Fox, N Katz, A Le and M Porkolab
MIT, PSFC, Cambridge, MA